1. Field of the Invention
This invention pertains to the preparation of fried snack foods, and particularly to a method for treatment of starch-containing sliced vegetables and doughs prior to frying so as to eliminate sticking of the slices during cooking without the addition of water to the slice.
2. Prior Art
Fried snack foods are a staple of the European and American diets. Such products are made from sliced vegetables, typically potatoes, or from doughs made from starch-containing grain flour to potato flakes. Potato chips are prepared commercially in automated plants using a number of processing machines, many of which have been patented (see U.S. Pat. Nos. 2,091,675 and 2,179,035) and by performing a number of common steps which have been the subject of frequent modification (see U.S. Pat. Nos. 2,611,705 and 4,283,437). Processes to make fried potato products directly from potatoes involve some combination of these basic steps: (1) peeling, (2) slicing, (3) washing, (4) frying in edible oils, and (5) seasoning. Characteristically, uncooked, unwashed slices or stampings are coated with a layer of starch which causes the individual pieces to stick to each other when they are allowed to come into contact with each other during handling, or deep fat frying. The resultant clump of food is unevenly cooked and must be removed from the commercial product. In addition, the direct frying of unwashed slices results in starch build-up in the cooking oil. The problem is particularly acute when the product if a french fried potato, shoestring potato, or potato chip made directly from the sliced, uncooked potato. It has become a long-standing practice in the industry to wash sliced starchy vegetables in warm water or brine to remove the surface starch prior to frying. While this procedure limits the clumping of the slices, water washing has several disadvantages. First, the washing results in a lower product yield because of the loss of starch and because of the mechanical breakage of the slices during handling. Second, the washing process adds water to the slice, which water must be removed prior to or during frying. Numerous inventions have been patented to remove the water prior to frying (for example, see U.S. Pat. No. 4,251,895 to Chardis). Since frying includes driving off surface and included water from the slice, the energy consumed in frying is directly related to the amount of water carried to the fryer. Finally, the wash water must be treated to remove starches and potato fragments before it can be discharged into the environment. There exists, therefore, a need for any process which will produce a commercially acceptable fried product without the need for a water wash of the uncooked slices.
Another undesired effect of the traditional methods for frying foods is the high percentage of lipid which remains in the final product. Typical fats and oils used in deep frying are triglycerides which are readily saponified and absorbed in the small intestine. Triglycerides provide twice the calories per gram of carbohydrates and proteins, and typical potato chips contain as much as 40% lipid by weight. Many of the alternative processes described for making foods which are similar in appearance to fried foods yield a product lower in lipid, but achieve the result by inclusion of more process steps, the addition of more ingredients, or by less efficient heat-transfer steps. For example, Murray (U.S. Pat. No. Re. 27,531) describes a process for recoating a blanched potato with amylose starch to provide a barrier to oil uptake. The result of these processes rarely has the uniquely satisfying taste, texture or appearance of a good potato chip, french fry, or similar food product.
A number of food-grade emulsifiers are compatible with cooking oils normally used in deep fat frying. Mono- and diglycerides are esters of glycerol which differ from typical fats and oils by being incompletely esterified. The resultant product has a hydrophobic component--the esterified part of the glycerol--and a hydrophilic component--the free hydroxyl(s)--at the other end of the molecule. These emulsifiers are digested by pathways analogous to that of fats and oils, but when present in a cooking oil, they allow the oil to dissolve a limited amount of water. Phospholipids are a class of compounds which are mixed esters of alcohols with ethanolamine derivatives and phosphoric acid. The most important phospholipids are the lecithins, mixed esters of glycerol and choline with fatty acids and phosphoric acid. Commercial lecithin is extracted from soybeans and usually includes cephalins and other trace natural products. Soybean lecithin is frequently used as an emulsifying agent in oleomargarine and mayonnaise, and in the formulation of the dough for many oven baked products. Polyglycerol esters are homologues of glycerides and retain most of their chemical and physical properties. They are used as emulsifiers where lower volatility is required.